Ubuntu Security and 2 nic's

[Gallagher, Tim (NE)]

I have an a Ubuntu setup with 2 nic's.  I have some computers trying to
communicate with a ip address that we filter out of our router.  I have
created a VLAN of the offending ip address and I now have eth0 on Ubuntu
box assigned to that IP. For logging purposes I want to be able to
connect to the box on another nic and see the traffic that is coming
into the nic with the offending ip.  I WANT to make sure that traffic is
not routed between the 2 nic's how can I do that.  I do not want any
routes or bridging to happen between the 2 nics.  Any advice on how to
do this?

Thanks,
-T